The long-range purpose of this project continues to be determination of the mechanism of action of drugs of abuse and the reasons why these drugs are used. Early in our studies, we learned that chronic users of marijuana refused to take it when in groups in which they could carry on a good conversation. Their reason for this was unclear. More recently, we have found that information learned under marijuana is better remembered when again under marijuana than when straight and vice versa. Last year we showed that marijuana selectively interferes with the left hemisphere's ability to process information . This year we showed that marijuana and alcohol differ in this respect. In a replication of previous findings, we found that marijuana depressed left hemisphere function while alcohol depressed both hemispheres. BIBLIOGRAPHIC REFERENCES: Stillman, R. C., Galanter, M., Fox, S., Lemberger, L., Weingartner, H. and Wyatt, R. J.: Metabolism and subjective effects of inahled delta 9-tetrahydrocannabinol under stress and no-stress conditions. Life Sci. 19: 569-576, 1976. Eich, J. E., Stillman, R. C., Weingartner, H., and Wyatt, R.J.: Some effects of repetition on state-dependent accessibility. Proceedings of the American Psychological Association, 1976.